1. Field of the Invention
The present invention relates to original-feeding devices.
2. Description of the Related Art
There is an increasing need for making copies and electronic data of various business forms used in offices. Accordingly, there is a demand for automatic original-conveying apparatuses capable of separating, conveying, and reading different kinds of originals at high speeds. An original-feeding device included in a typical automatic original-conveying apparatus basically includes a separator configured to separate one of stacked originals from the others and a feeder configured to feed an original to the separator. Such separators and feeders employ various methods, for example, a separation method employing a separation pad, and a retard separation method that provides a high conveyability in the conveyance of a cardboard and the like.
FIG. 8 is a schematic diagram showing transmission paths for drive signals and control signals in a typical original-feeding device of a retard-separation type. An original tray 501 receives one or more originals. A swing arm 510, functioning as a moving member, swingable about a support is provided above the original tray 501. The swing arm 510 has at an end thereof a pickup roller 502, functioning as an original feeder, configured to be in contact with the top one of the originals on the original tray 501 and to be rotatable in a direction in which the original is fed. The pickup roller 502 can be moved by the swing arm 510, configured to swing with a driving force transmitted from a pickup motor 539, between a pressing position and a retracted position. At the pressing position, the pickup roller 502 is pressed against the originals on the original tray 501 and feeds an original. At the retracted position, the pickup roller 502 is spaced apart from the originals. A pair of separation rollers 503, functioning as a separator, consists of a feed roller 504 and a retard roller 505 and is provided on the downstream side in the feed direction with respect to the pickup roller 502. The pair of separation rollers 503 conveys the original fed thereto further to the downstream side. The retard roller 505 is pressed against the feed roller 504 and receives a rotational driving force acting in such a direction as to feed back the original toward the original tray 501. If a plurality of originals are fed by the pickup roller 502, one of the originals is separated from the others while such originals are conveyed through and nipped by the pair of separation rollers 503. The rollers 504 and 505 are driven to rotate with driving forces transmitted from a single motor 537. The driving force for rotating the retard roller 505 is transmitted through a torque limiter (not shown) so that the retard roller 505 rotates in the direction opposite to the direction in which the original is conveyed. When the feed roller 504 pressed against the retard roller 505 is rotated in the conveyance direction, a torque acting in the conveyance direction is applied to the retard roller 505. The torque set in the torque limiter is smaller than that applied by the feed roller 504 to the retard roller 505. Therefore, when the feed roller 504 rotates, the retard roller 505 follows the rotation of the feed roller 504, thereby rotating in the conveyance direction. The pickup roller 502 often feeds two or more originals to the pair of separation rollers 503 (such a situation is referred to as multiple feeding). In such a situation, the coefficient of friction produced between the two or more originals is smaller than the coefficient of friction produced between the retard roller 505 and one of the originals. Therefore, the retard roller 505 receiving the driving force from the torque limiter acting in the direction opposite to the conveyance direction rotates in the direction opposite to the conveyance direction. Consequently, all the originals but the one at the top are fed back toward the original tray 501. Thus, the originals are conveyed one by one toward an image-forming device.
Usually, the pickup roller 502 is moved away from the originals at a predetermined timing after an original-feeding operation is started. When a sensor 511 detects the trailing edge of an original, the pickup roller 502 is brought into contact with the stack of originals for a subsequent feeding operation. An exemplary technique for increasing the number of conveyable originals per unit time is disclosed in Japanese Patent Laid-Open No. 2001-146329. In this technique, the timing at which the trailing edge of an original is released from the pair of separation rollers 503 is estimated from the length of the original and the time required for bringing the pickup roller 502 into contact with the stack of originals, and the pickup roller 502 is brought into contact with the stack of originals at the estimated timing.
There is a known automatic original-conveying apparatus having a function called a different-sized-originals conveyance mode in which each of a plurality of originals is subjected to size detection and is processed in accordance with the detected size. If the different-sized-originals conveyance mode is not set, processing is performed regardless of the sizes of the originals, that is, all the originals are treated as being of the same size. For example, all originals are treated as being of a size detected for a first original or a size designated by a user.
To improve the productivity in terms of original reading (the number of readable originals per unit time), the pickup roller 502 needs to be lowered as soon as possible after the separation of originals so as to be ready for a subsequent feeding operation. In the technique disclosed in Japanese Patent Laid-Open No. 2001-146329, if the different-sized-originals conveyance mode is not set, the pickup roller 502 is lowered before the trailing edge of an original passes the sensor 511, whereby the productivity is improved.
If, however, a stack of originals includes any originals having different lengths from the others despite the different-sized-originals conveyance mode not being set, the pickup roller 502 may be in contact with the stack of originals at a position deviated from the expected position.
FIGS. 9A and 9B show exemplary behavior of originals after the pickup roller 502 is lowered at a timing at which the trailing edge of an (N−1)-th original is assumed to have been released from the pair of separation rollers 503 in a case where an N-th original is of the A4 size and the (N−1)-th original is of the A3 size. In this case, to suppress the reduction in durability of the retard roller 505, the motor 537 is stopped immediately before the trailing edge of the (N−1)-th original (assumed to be of the A4 size) is assumed to be released from the pair of separation rollers 503. Therefore, in FIG. 9A, the (N−1)-th original is being conveyed by a pair of rollers 506 driven by a motor 538, and the pair of separation rollers 503 are rotating in the conveyance direction, following the movement of the (N−1)-th original. Meanwhile, the pickup roller 502 whose rotation is stopped is in contact with the (N−1)-th original. Under the weight of the pickup roller 502, a frictional force is produced between the (N−1)-th original and the N-th original. Consequently, as in FIG. 9B, the N-th original is dragged by the (N−1)-th original and may pass through the pair of separation rollers 503, that is, multiple feeding may occur.
FIGS. 10A to 10C show the behavior of the trailing edge of an (N−1)-th original in a case where an N-th original is of the A3 size and the (N−1)-th original is of the A4 size. In FIG. 10A, if the coefficient of friction produced between the (N−1)-th original and the N-th original is large, the N-th original is dragged to a position near the pair of separation rollers 503 by the (N−1)-th original. Besides, if the leading edge of the N-th original is folded or curled as in FIG. 10B, the N-th original may be drawn in by the feed roller 504 as in FIG. 10C. Consequently, the interval between the (N−1)-th original and the N-th original may be reduced, resulting in the possibility of a jam.
Thus, an automatic original-conveying apparatus of the retard-separation type employing the technique disclosed in Japanese Patent Laid-Open No. 2001-146329 for improvement of productivity in terms of original reading occasionally causes multiple feeding and jams if a stack of originals includes any originals having different lengths from the others.